The present invention relates generally to control systems for aircraft engines, and more particularly relates to engine control systems having redundant mechanical components.
Typically, a fuel metering unit regulates the flow of fuel to the combuster of the engine. The fuel metering unit may include an electrohydraulic servo valve (EHSV) which controls a fuel metering valve to regulate the fuel flow to the engine. It is also common to utilize other electrohydraulic servo valves to regulate other engine parameters, such as compressor variable geometry and fan variable geometry for positioning the vanes of the engine. To ensure control over these systems and of the engine, redundant electronics are employed, which typically consist of back-up electric coils in the EHSVs. The engine computer control will switch to the back-up coil for control over the system in the unlikely event the primary coil fails. In this architecture, electronic reduncancy is provided but the hydromechanical aspects are single thread.
In some aircraft engine applications, it has been found desirable to provide hydromechanical back-up in addition to electrical back-up. That is, an entire secondaryelectrohydraulic servo valve is supplied for each primary electrohydraulic servo valve. For example, there is a redundant or secondary electrohydraulic servo valve connected to operate the fuel metering valve in the event the primary electrohydraulic servo valve fails. Therefore, the system for transferring the control from a primary EHSV to a secondary EHSV now has hydromechanical as well as electronic requirements.
One embodiment of the present invention provides a switching system for an engine having redundant control components. The switching system generally comprises an actuator, a control system, inlet and outlet lines, and a transfer valve. The actuator is operable to control an engine parameter. The control system includes a first electrohydraulic servo valve and a second electrohydraulic servo valve, the first and second servo valves being fluidically connected to the actuator for operating the actuator. The inlet line supplies pressurized fluid and the outlet line drains fluid. The transfer valve is positioned between the first and second servo valves and the inlet and outlet lines. The transfer valve is operable between a first position linking the first servo valve to the inlet and outlet lines, and a second position linking the second servo valve to the inlet and outlet lines.
According to more detailed aspects of this embodiment, the switching system may further comprise a second actuator and a second control system. The second actuator is operable to control a second engine parameter. The second control system has a third electrohydraulic servo valve and a fourth electrohydraulic servo valve, the third and fourth servo valves being fluidically connected to the second actuator for operating the second actuator. The transfer valve is positioned between the third and fourth servo valves and the inlet and outlet lines. The first position of the transfer valve links the third servo valve to the inlet and outlet lines, while the second position of the transfer valve links the fourth servo valve to the inlet and outlet lines.
Similarly, the switching system may further comprise a third actuator and a third control system. The third actuator is operable to control a third engine parameter. The third control system has a fifth electrohydraulic servo valve and a sixth electrohydraulic servo valve, the fifth and sixth servo valves being fluidically connected to the third actuator for operating the third actuator. The transfer valve is positioned between the fifth and sixth servo valves and the inlet and outlet lines. The first position of the transfer valve links the fifth servo valve to the inlet and outlet lines, while the second position of the transfer valve links the sixth servo valve to the inlet and outlet lines.
Preferably, the actuator is a fuel metering valve for regulating fuel flow to the engine. Alternately, the actuator controls compressor variable geometry or fan variable geometry. Most preferably, the actuator is a fuel metering valve for regulating fuel flow to the engine, the second actuator controls compressor variable geometry, and the third actuator controls fan variable geometry. According to other aspects of the embodiment, the inlet line is bifurcated to supply fluid at a first pressure Psf and a second pressure Pc. The transfer valve supplies fluid at Pc to the servo valves of the first control system, and the transfer valve supplies fluid at Psf to the servo valves of the second control system.
According to another embodiment of the present invention, a switching valve is provided for switching between a primary electrohydraulic servo valve and a backup electrohydraulic servo valve of at least one control system. The servo valves are operatively connected to at least one actuator for controlling at least one engine parameter. The servo valves receive pressurized fluid from an inlet and discharge fluid to an outlet. The switching valve generally comprises a transfer valve assembly including a valve body positioned within a valve sleeve. The transfer valve assembly is interposed between the servo valves and the inlet and outlet to regulate communication between the servo valves and the inlet and outlet. The valve body is moveable within the valve sleeve to a first position linking the primary servo valve to the inlet and outlet. Further, the valve body is moveable within the valve sleeve to a second position linking the backup servo valve to the inlet and outlet. Preferably, the valve body includes at least one annulus for connecting the at least one control system to the inlet, and the valve body includes an annulus for connecting the at least one control system to the outlet.
According to yet another embodiment of the present invention, a switching system is provided for an engine having redundant control components for multiple control systems. The switching system generally comprises an inlet for supplying pressurized fuel, and an outlet for draining fuel. A first primary electrohydraulic servo valve is operatively connected to a fuel metering valve to regulate fuel flow. A first backup electrohydraulic servo valve is operatively connected to the fuel metering valve. A second primary electrohydraulic servo valve is operatively connected to an actuator to control an engine parameter. A second backup electrohydraulic servo valve is operatively connected to the actuator. Finally, a transfer valve is positioned between the servo valves and the inlet and outlet, the transfer valve being operable between a first position supplying the first and second primary servo valves with fuel, and a second position supplying the first and second backup servo valves with fuel.
Preferably, the inlet includes two lines supplying fuel at a first pressure Psf and a second pressure Pc. The first primary and first backup servo valves utilize fuel at Pc, and the second primary and second backup servo valves utilize fuel at Psf The transfer valve includes a first annulus for supplying fuel at Pc to one of the first primary and first backup servo valves, and the transfer valve includes a second annulus for supplying fuel at Psf to one of the second primary and second backup servo valves. The transfer valve preferably includes a third annulus for draining fuel at pressure P0 from the first and second primary servo valves or the first and second backup servo valves. The fuel metering unit may further comprise a third primary electrohydraulic servo valve operatively connected to a second actuator to control a second engine parameter and a third backup electrohydraulic servo valve operatively connected to the second actuator.
According to still another embodiment of the present invention, a method is provided for switching between the primary electrohydraulic servo valves and the secondary electrohydraulic servo valves of multiple control systems controlling various engine parameters. An inlet and an outlet supply and drain fluid to and from the control systems. The method comprises the steps of: providing a transfer valve between the servo valves and the inlet and outlet; and operating the transfer valve between two positions including a first position and a second position, the first position supplying fluid to and draining fluid from the primary servo valves, the second position supplying fluid to and draining fluid from the secondary servo valves. Preferably, the method further comprises the step of providing the transfer valve with an annulus for each different supply pressure utilized by the multiple control systems.